<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <script>
        /*
            =
            可以将负号右侧的值赋值给负号左侧的变量
            +=
                a+=5等于a=a+5
        */
        var a=10;
        a=a+5;
        a-=5;
        console.log(a);
    </script>
</head>
<body>
    
</body>
</html>